Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address and servo bursts) which is read by the head and processed by a servo control system to control the velocity of the actuator arm as it seeks from track to track.
Various patterns have been employed to record the servo bursts in the servo sectors, such as a quadrature (A,B,C,D) servo pattern comprising squared bursts of transitions each recorded at a precise interval and offset from a servo track centerline. A position error signal (PES) is generated by demodulating and comparing the amplitude of each servo burst (A,B,C,D) relative to one another. Another known servo pattern comprises slanted line servo bursts recorded at a tilt angle with respect to the preamble of the servo sector. The PES is generated by comparing a phase difference between the preamble signal and the burst signal generated as the head passes over the slanted lines.